It has been established that anti-phagocytic surface antigens play a major role in the invasiveness of most pyogenic bacteria. One exception to this rule was Staphylococcus aureus, for only in a few instances had a chemically defined anti-phagocytic antigen been isolated from these organisms. However, evidence is now accumulating which indicates that clinical isolates of S. aureus do possess a diversity of immunologically significant antigens, namely acidic polysaccharides and proteins, mucopeptide-protein complexes, and protein A. In view of these observations, it is feasible to assume that a systematic scheme for the classification of pathogenic S. aureus could be established which would be based on some of these surface antigens. Such a scheme may be useful in the elucidation of the biological and immunological relationships which exist among the various clinical isolates of S. aureus. In addition, knowledge of the cellular mosaic of S. aureus may facilitate the development of a more effective means of immunological therapy for susceptible individuals. Therefore, the purpose of this study is to isolate, purify and immunochemically characterize the surface antigens of clinical isolates of S. aureus. Special emphasis will be made to separate the various constituents of the surface structures of S. aureus, namely the acidic polysaccharides, the acidic proteins, and "aggressin" (mucopeptide-protein complex). The biological significance of these antigens will be analyzed. For example, the anti-phagocytic capacity of these antigens will be tested by the in vitro phagocytic test. The inhibition of the staphylococcal adherence onto mammary bovine mucosal surfaces will be attempted by the use of these purified antigens. Attempts will made to isolate and purify the lesion-enhancing component and to determine its effect on the alternate complement pathway as well as its possible role as a lymphocytic mitogen. In addition, the capacity of the mucopeptide-protein complex to inhibit in vitro phagocytosis will be tested. BIBLIOGRAPHIC REFERENCE: Kane, J. A. and W. W. Karakawa. Multiple polysaccharide antigens of group B streptococcus, type Ia: Emphasis on a sialic acid type-specific polysaccharide. J. Immunol., (June, 1977).